Not a real answer.
Because it makes it easier to reach the cue ball would be an answer.
Sometimes a cue maker makes "x" length....take it or leave it.
Sometimes a customer likes a longer cue because they like the "perception" difference with a longer shaft....cue ball to object ball looks more similar in size opposed to cue ball looking a bit larger when using a short cue/bridge.
Sometimes a customer likes extra weight upfront without adding unnatural materials such as weight bolts etc...etc...
Sometimes a person may "have to have" a longer cue after injuries cause them to lose the ability to bend as low as before.
There are a ton of reasons.
IMO, if a person doesn't know at least some of them they are either in great health or they have never took the time to actually experiment to see for themselves.
Try it, you may like it. Then again, you may not and can go back to a shorter cue.
BTW, my cue length is determined by my health at the time. If my back and neck are hurting worse, I use a longer cue. If I'm doing at least "ok", I'll use a shorter cue.
Jeff